Citrus growers I need some help!

in Fruit & veg
I recently had a crazy Covid moment and bought a lemon and orange tree, I have no idea what I am doing but am determined not to kill them this year. They are alleged to be 3-4' high in 6.5L pots and hardy down to 5C.
I have a couple of pressing questions:
I am concerned that the pots sound a bit small for the trees so how soon should I think of re-potting them (if at all) and what size pot would be sensible?
It is unlikely I can get any JI2 in the near future so would a mixture of garden soil, mpc, grit, vermiculite and sand be suitable?
I have reprimanded myself severely for this moment of madness but would really appreciate any help since what is done is done
I have a couple of pressing questions:
I am concerned that the pots sound a bit small for the trees so how soon should I think of re-potting them (if at all) and what size pot would be sensible?
It is unlikely I can get any JI2 in the near future so would a mixture of garden soil, mpc, grit, vermiculite and sand be suitable?
I have reprimanded myself severely for this moment of madness but would really appreciate any help since what is done is done

"The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it." Sir Terry Pratchett
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Have a read of this - https://www.rhs.org.uk/advice/grow-your-own/fruit/citrus
I guess I'l have to mix my own and hope. I am hoping my unheated greenhouse will be enough (with added bubble wrap) to see them through the winter. The citrus food should be coming with the trees.
They get citrus fertiliser and I've also given them some slow release tomato fertiliser this summer and, so far, flowering and pollinating are going well and I have small fruits forming on both. I have their pots in saucers so the water doesn't just run thru and I can see when the saucers are bone dry and give them more water but I do have them sat on the steps at the front of the house, full south and 40C these last few days so they get thirsty.
I also have a young yuzu which is yet to flower and, I have discovered, prefers ericaceous compost so next time I'm buying compost I'll get some and re-pot it.